ABSTRACT
The mammalian Ajuba LIM proteins (Ajuba, LIMD1, and WTIP) are adaptor proteins that exhibit the potential to communicate cell adhesive events with nuclear responses to remodel epithelia. Determining their role in vivo, however, has been challenging due to overlapping tissue expression and functional redundancy. Thus, we turned to Drosophila, where a single gene, CG11063 or djub, exists. Drosophila lacking the djub gene or depleted of dJub by RNA interference identify djub as an essential gene for development and a novel regulator of epithelial organ size as a component of the conserved Hippo (Hpo) pathway, which has been implicated in both tissue size control and cancer development. djub-deficient tissues were small and had decreased cell numbers as a result of increased apoptosis and decreased proliferation, due to downregulation of DIAP1 and cyclin E. This phenocopies tissues deficient for Yorkie (Yki), the downstream target of the Hippo pathway. djub genetically interacts with the Hippo pathway, and epistasis suggests that djub lies downstream of hpo. In mammalian and Drosophila cells, Ajuba LIM proteins/dJub interact with LATS/Warts (Wts) and WW45/Sav to inhibit phosphorylation of YAP/Yki. This work describes a novel role for the Ajuba LIM proteins as negative regulators of the Hippo signaling pathway.
Subject(s)
Drosophila Proteins/physiology , Homeodomain Proteins/physiology , Intracellular Signaling Peptides and Proteins/physiology , Protein Serine-Threonine Kinases/physiology , Adaptor Proteins, Signal Transducing/genetics , Adaptor Proteins, Signal Transducing/physiology , Animals , Animals, Genetically Modified , Apoptosis , Cell Proliferation , Drosophila/genetics , Drosophila/growth & development , Drosophila/physiology , Drosophila Proteins/genetics , Epistasis, Genetic , Eye/cytology , Eye/growth & development , Genes, Insect , Homeodomain Proteins/genetics , Humans , Intracellular Signaling Peptides and Proteins/genetics , Mammals , Models, Biological , Mutation , Nuclear Proteins/genetics , Nuclear Proteins/physiology , Organ Size , Protein Kinases/genetics , Protein Kinases/physiology , Protein Serine-Threonine Kinases/genetics , RNA Interference , Signal Transduction , Species Specificity , Trans-Activators/genetics , Trans-Activators/physiology , YAP-Signaling ProteinsABSTRACT
Correct cellular patterning is central to tissue morphogenesis, but the role of epithelial junctions in this process is not well-understood. The Drosophila pupal eye provides a sensitive and accessible model for testing the role of junction-associated proteins in cells that undergo dynamic and coordinated movements during development. Mutations in polychaetoid (pyd), the Drosophila homologue of Zonula Occludens-1, are characterized by two phenotypes visible in the adult fly: increased sensory bristle number and the formation of a rough eye produced by poorly arranged ommatidia. We found that Pyd was localized to the adherens junction in cells of the developing pupal retina. Reducing Pyd function in the pupal eye resulted in mis-patterning of the interommatidial cells and a failure to consistently switch cone cell contacts from an anterior-posterior to an equatorial-polar orientation. Levels of Roughest, DE-Cadherin and several other adherens junction-associated proteins were increased at the membrane when Pyd protein was reduced. Further, both over-expression and mutations in several junction-associated proteins greatly enhanced the patterning defects caused by reduction of Pyd. Our results suggest that Pyd modulates adherens junction strength and Roughest-mediated preferential cell adhesion.
Subject(s)
Adherens Junctions/metabolism , Body Patterning , Cell Adhesion/physiology , Drosophila Proteins/metabolism , Drosophila melanogaster , Membrane Proteins/metabolism , Phosphoproteins/metabolism , Pupa/anatomy & histology , Animals , Cadherins/genetics , Cadherins/metabolism , Cell Adhesion Molecules/genetics , Cell Adhesion Molecules/metabolism , Cell Adhesion Molecules, Neuronal/genetics , Cell Adhesion Molecules, Neuronal/metabolism , Drosophila Proteins/genetics , Drosophila melanogaster/anatomy & histology , Drosophila melanogaster/embryology , Drosophila melanogaster/metabolism , Eye Proteins/genetics , Eye Proteins/metabolism , Membrane Proteins/genetics , Morphogenesis , Phosphoproteins/genetics , Photoreceptor Cells, Invertebrate/cytology , Photoreceptor Cells, Invertebrate/embryology , Pupa/metabolism , RNA Interference , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Retina/cytology , Retina/embryology , Signal Transduction/physiology , Tight Junction Proteins , Wings, Animal/anatomy & histology , Wings, Animal/embryology , Zonula Occludens-1 Protein , alpha Catenin/genetics , alpha Catenin/metabolismABSTRACT
Developing tissues require cells to undergo intricate processes to shift into appropriate niches. This requires a functional connection between adhesion-mediating events at the cell surface and a cytoskeletal reorganization to permit directed movement. A small number of proteins are proposed to link these processes. Here, we identify one candidate, Cindr, the sole Drosophila melanogaster member of the CD2AP/CIN85 family (this family has been previously implicated in a variety of processes). Using D. melanogaster retina, we demonstrate that Cindr links cell surface junctions (E-cadherin) and adhesion (Roughest) with multiple components of the actin cytoskeleton. Reducing cindr activity leads to defects in local cell movement and, consequently, tissue patterning and cell death. Cindr activity is required for normal localization of Drosophila E-cadherin and Roughest, and we show additional physical and functional links to multiple components of the actin cytoskeleton, including the actin-capping proteins capping protein alpha and capping protein beta. Together, these data demonstrate that Cindr is involved in dynamic cell rearrangement in an emerging epithelium.
